arm64: spectre: Rename spectre_v4_patch_fw_mitigation_conduit

The spectre-v4 sequence includes an SMC from the assembly entry code.
spectre_v4_patch_fw_mitigation_conduit is the patching callback that
generates an HVC or SMC depending on the SMCCC conduit type.

As this isn't specific to spectre-v4, rename it
smccc_patch_fw_mitigation_conduit so it can be re-used.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>